Slip clutch for roller shade

ABSTRACT

A slip clutch for a roller blind. The slip clutch comprises a clutch base with a shaft portion, a drive sprocket including a drive tube and rotationally mounted on the clutch base, at least one clutch spring and a roller tube connector. The clutch spring is in the form of a coil spring frictionally engaged about the shaft portion and positioned between the shaft portion and the drive tube. The spring includes end members that engage the drive tube such that rotation of the drive tube about the shaft portion is resisted by the frictional engagement of the spring about the shaft. Rotation of the drive tube in either direction causes the drive tube to apply a force to the clutch spring in a direction such that encourages an increase in the diameter of the spring to reduce the frictional engagement of the clutch spring with the shaft portion.

BACKGROUND OF THE INVENTION

Roller shades, or roller blinds as they are sometimes referred to, arecommonly mounted on windows for privacy purposes and to limit lightintrusion. Modern roller shades typically employ a clutch mechanism thatpermits the shade to be raised and lowered through pulling on one end ofa looped chain or cord and that is received around the clutch. Theclutch serves as a mechanism to impart rotational movement to the rollertube of the blind when the chain or cord is pulled in one direction orthe other. Typically, the clutch is also utilized to retain the rollertube in a locked position when a desired amount of fabric has beenunrolled therefrom. That is, in some instances it will be desirable to“lower” the shade such that its fabric covers the entire window, whilein other instances it may be desirable to only cover the upper portionof the window. In either case, once the desired amount of fabric hasbeen unrolled from the roller tube, the clutch assists in maintainingthe tube in position without winding or unwinding more fabric until theoperator again applies tension to one end of the cord or chain.

The clutch mechanism of a roller shade or blind therefore allows forclockwise or counterclockwise rotation of the roller tube upon theapplication of tension to the blind's cord or chain, while maintainingthe tube in position when no, or insufficient, tension is applied. Sincethe clutch is an integral component of the roller shade, there is aconstant need to improve the clutch in order to enhance the experienceand operational options available to a user when lowering the shade.

SUMMARY OF THE INVENTION

The invention therefore provides a slip clutch for a roller blind, theslip clutch comprising a clutch base, said clutch base including a shaftportion; a drive sprocket rotationally mounted on said clutch base, saiddrive sprocket engageable with a chain or cord that operate to impartrotational movement to said drive sprocket, said drive sprocketincluding a drive tube receivable about said shaft portion of saidclutch base; at least one clutch spring, said clutch spring in the formof a coil spring frictionally engaged about said shaft portion of saidclutch base and positioned between said shaft portion and said drivetube, said spring including end members that engage said drive tube suchthat rotation of said drive tube about said shaft portion is resisted bythe frictional engagement of said clutch spring about said shaftportion; a roller tube connector secured about said drive tube such thatsaid roller tube connector and said drive tube rotate together aboutsaid shaft portion, said roller tube connector free from contact withsaid clutch spring, rotation of said drive tube in either directioncausing said drive tube to apply a force to said clutch spring in adirection such that encourages an increase in the diameter of saidspring to thereby reduce the frictional engagement of said clutch springwith said shaft portion.

Further aspects of the invention will become apparent from the followingdescription taken together with the accompanying drawings.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example, to the accompanying drawings which show exemplaryembodiments of the present invention in which:

FIG. 1 is a side elevational view of a typical roller shade having itsend brackets removed;

FIG. 2 is an exploded side perspective view of the roller shade of FIG.1;

FIG. 3 is an upper side perspective view of a slip clutch constructed inaccordance with the prior art;

FIG. 4 is an end view of the clutch shown in FIG. 3;

FIG. 5 is an end perspective view of the roller tube housing connectorof the roller shade;

FIG. 6 is a side perspective exploded view of the slip clutch inaccordance with an embodiment of the present invention;

FIG. 7 is a side elevational view of FIG. 6;

FIG. 8 is an upper end perspective view of the slip clutch shown in FIG.6 in its assembled form;

FIG. 9 is an inner end view of the slip clutch shown in FIG. 8;

FIG. 10 is a schematic view of the inner end of the slip clutch of FIG.9 showing the positioning and configuration of the components of theclutch during clockwise rotation; and

FIG. 11 is a view similar to FIG. 10 showing the components andconfiguration of the clutch during counterclockwise rotation.

DETAILED DESCRIPTION

The present invention may be embodied in a number of different forms.The specification and drawings that follow describe and disclose some ofthe specific forms of the invention.

FIG. 1 shows, in general, a typical roller blind or roller shade 1having been removed from its end brackets. Roller blind 1 includes blindfabric 2 received over a roller tube 3 that is driven by a clutchmechanism 4 activated by a chain or cord 5. In FIG. 2 there is shown theidler end connector 6 of roller tube 3 and a typical spring assistmechanism 7 as would commonly be used in many roller blinds. Clutch 4 isa slip clutch that permits the rotation of roller tube 3 in order towind or unwind fabric thereabout, but that also prevents rotation of thetube when a desired amount of blind fabric has been received on theroller tube or has been lowered downwardly over the window. Referring toFIGS. 6 and 7 there is shown in exploded view an embodiment of slipclutch 4 constructed in accordance with the invention. Here, slip clutch4 is generally comprised of a clutch base 8, a drive sprocket 9, asprocket cover 10, a clutch spring 11, and a roller tube connector 12.When assembled, each of the above mentioned parts nest together in agenerally coaxial configuration and are received about a locking pin 13,which serves to maintain the components in their desired position.

With reference again to FIGS. 6 and 7, clutch base 8 can be seen asincluding a rear plate portion 14 and a shaft portion 15. Shaft portion15 preferably has a hollow bore for receiving locking pin 13. Drivesprocket 9 includes a drive wheel or cog 16 that is designed to receivea chain or cord that is used to impart rotational movement to thesprocket. Connected to the drive wheel or cog is a drive tube 17. Drivesprocket 9 is rotationally mounted upon clutch base 8 through thereceipt of shaft portion 15 within drive tube 17. Sprocket cover 10 isthen received over drive tube 17 and engages rear plate 14 of the clutchbase in order to form an interior pocket or cavity that receives andretains the chain or cord.

Clutch spring 11 is preferably in the form of a coil spring that isreceived about the exterior surface of shaft portion 15 and that isfrictionally engaged therewith. As shown in the attached drawings, andmore particularly in FIGS. 8 and 9, drive tube 17 and shaft portion 15are dimensioned such that clutch spring 11 is positioned between theshaft portion and the drive tube. Further, clutch spring 11 includes apair of end members, 18 and 19, respectively, that engage drive tube 17such that rotation of the drive tube about the shaft portion is resistedby engagement of end members 18 and 19 with drive tube 17 and by thefrictional engagement of the clutch spring about shaft portion 15.

In the embodiment of the invention shown, the engagement of end members18 and 19 with drive tube 17 is achieved through the formation of afirst axially oriented slot 20 within the exterior of drive tube 17. Endmembers 18 and 19 will thus be comprised of upwardly and outwardly bentends that extend at approximately right angles from the surface of shaftportion 15. The radial distance between end members 18 and 19 is suchthat it is less than the radial opening of first axial slot 20 so thatrotation of the drive tube will result in engagement of the drive tubewith only one of end members 18 and 19 at any one particular time.Further, the winding of the coils of clutch spring 11 are preferably ina direction that causes the drive tube to apply a force to the clutchspring (through the engagement of one of ends 18 or 19 with an edge ofslot 20) in a direction that encourages an increase in the diameter ofthe spring. That is, the windings are such that when one side or edge offirst axial slot 20 engages one of end members 18 or 19, furtherrotation of the drive tube will have a tendency to “open” the clutchspring, which will encourage an increase in the diameter of the spring,thereby reducing its frictional engagement with shaft portion 15. Thatis, through the application of a rotational force to the drive sprocket(by means of pulling on one end of the chain or cord receivedthereabout) first axial slot 20 will be caused to contact one of endmembers 18 and 19. The frictional engagement of the clutch spring withshaft portion 15 will resist movement of the drive sprocket until suchtime as the force applied to the sprocket is able to overcome thefrictional engagement of the clutch spring.

The ends of the clutch spring and the sides of first axial slot 20 aresuch that the application of a rotational force to the clutch spring,through operation of the chain or cord, exhibits a tendency to reducethe frictional engagement of the clutch spring upon shaft portion 15 (by“opening” the spring), thereby making rotation of the clutch (and, aswill be explained below, the roller tube) easier for the operator. Sincethe width of first axial slot 20 is greater than the spacing between endmembers 18 and 19, rotation of drive sprocket 9 in either direction willenable only one of the end members to be contacted by the drive tube atany one time. In that manner, rotation of the drive sprocket in either aclockwise or counter-clockwise direction will enable an “opening” forceto be applied to the clutch spring regardless of whether it is desiredto lift or lower the blind fabric.

With specific reference to FIGS. 5 through 9, roller tube connector 12is shown as having a generally hollow interior that is received aboutthe exterior surface of drive tube 17. A centrally positioned hollowtube portion 21 extends through roller tube connector 12 and is receivedthrough shaft portion 15 of the clutch base to ensure coaxial alignmentof the various components, and to permit the receipt of locking pin 13therethrough. Roller tube connector 12 is secured to drive tube 17 in amanner that prevents contact between the roller tube connector and theclutch spring. In the embodiment shown, the means of connecting rollertube connector 12 to the drive tube 17 so that the roller tube connectoris free from contact with the clutch spring is through the formation ofa second axially oriented slot 22 within drive tube 17. Second slot 22receives a tab 23 that is positioned upon the interior surface of rollertube connector 12 such that the roller tube connector and the drive tubeare effectively locked together and rotate in unison. Such a structure(that locks the roller tube connector and the drive tube together in thedescribed manner) is a significant departure from existing clutches asprior clutches (see FIGS. 3 and 4) permit contact between the rollertube connector and the clutch spring. In prior clutches, tab 23 ispositioned between spring end members 18 and 19 and results in theapplication of force to the spring in a direction that has a tendency tosqueeze or contract the diameter of the clutch spring, thereby tendingto increase the frictional contact between the spring and the shaftportion of the clutch base, effectively making the clutch a “non-slip”clutch.

It will thus be appreciated and understood that in light of the abovedescribed structure there will be no application of a force to theclutch spring which would otherwise have a tendency to increase thefrictional contact between the spring and shaft portion 15 of clutchbase 8.

In most embodiments it is expected that roller tube connector 12 will beformed from a form of plastic, fibreglass, polycarbonate or othergenerally similar material. Accordingly, in order to enhance thestrength and rigidity of tab 23 the tab itself may be formed form ametal or metal-like material or, alternatively, the tab may be coveredwith a metal plate or clip. Further, in one of the preferred embodimentsof the invention the interior surface of drive tube 17, with theexception of that portion that has been removed to form first axial slot20, may be encased by a metallic bushing 24. The ends of bushing 24preferably extend around the edges of first axial slot 20 to present astrong and rigid edge surface against which end members 18 and 19 ofclutch spring 11 can bear. That is, in many instances it is expectedthat the drive sprocket and its drive tube will be formed from a plasticor other similar material. Accordingly, through the incorporation of ametal bushing having edges that encompass the sides of first axial slot20, the tendency for end members 18 and 19 of the clutch spring todeform the edges of first axial slot 20 is eliminated or significantlyreduced. Bushing 24 also prevents unintended contact between tab 23 andclutch spring 11 that could possibly occur (for example, if there were asignificant twisting or side load applied to the roller tube).

In a further embodiment of the invention (not shown) two or more clutchsprings may be utilized. The incorporation of multiple clutch springsmay be particularly advantageous in situations where the load to beborne by the clutch is significant, as would be the case in long blindsor blinds that incorporate heavy fabrics.

From a thorough understanding of the invention it will be appreciatedthat slip clutch 4 presents the ability to prevent rotational movementof a roller tube when desired. When an operator wishes to rotate theroller tube for purposes of either unrolling fabric or rewinding thefabric upon the roller tube, pulling the drive chain or cord in eitherdirection will result in rotational force being imparted to drivesprocket 9. As the drive sprocket rotates, one of the longitudinal edgesof first axial slot 20 will contact one of the ends 18 and 19 of clutchspring 11. Once the rotational force applied to the drive sprocketexceeds the frictional force of the clutch spring upon the shaft portionof the clutch base, the drive sprocket will rotate, in unison withroller tube connector 12, causing the roller tube to rotate in either aclockwise or counter-clockwise direction. As indicated above, theapplication of the rotational force to one of end members 18 or 19 ofthe clutch spring will have a tendency to apply an “opening” force tothe spring, which in most instances will result in rotation of the drivesprocket becoming easier for the operator. With the roller tubeconnector 12 being free from contact with the clutch spring, there is nofriction enhancing force applied to the clutch spring which wouldotherwise make rotating the drive sprocket more difficult and requirethe individual to pull significantly harder on the cord or chain. Oncethe chain or cord is released, the force tending to “open” the spring isremoved, causing the spring to contract to its rest configuration andeffectively locking the clutch, and the roller tube in position.

Similarly, from an understanding of the described structure it will beunderstood that, unlike in the case of traditional clutches, the slipclutch of the present invention will also permit an operator to “lower”the blind (ie unwind fabric from the roller tube) through merelygrasping the bottom bar or bottom of the fabric and pulling downwardly.Whereas in the case of a traditional clutch pulling on the bottom of thefabric will have little or no effect (unless sufficient force wasapplied to damage the clutch), through use of the above described slipclutch, pulling on the bottom of the fabric will result in roller tubeconnector 12 applying a rotational force to drive tube 17 that will tendto “open” the clutch spring, facilitating rotational movement of theroller tube and an unwinding of the fabric. Hence the slip clutch of thepresent invention provides an operator with the added advantage of beingable to lower the blind fabric through merely grasping the bottom of thefabric and pulling in a downward direction. That result is accomplishedthrough the use of a structure that is not only robust and durable, butthat has relatively consistent torque requirements throughout itsoperation, again unlike many traditionally available clutches.

Clutch 4 may be constructed in a manner where its internal friction issuch that the clutch effectively works together with spring assistmechanism 7 to generally “balance” the weight of the blind fabric. Thatis, the fabric unwound from the roller tube will generally be held bythe spring assist mechanism with the slip clutch helping to balance thetorque difference between torque generated by the blind fabric and thatgenerated by the spring assist. In this way, the amount of force neededto be applied via the drive chain or cord, or through pulling downwardlyon the blind fabric, is minimized and relatively consistent.

It is to be understood that what has been described are the preferredembodiments of the invention. The scope of the claims should not belimited by the preferred embodiments set forth above, but should begiven the broadest interpretation consistent with the description as awhole.

The invention claimed is:
 1. A slip clutch for a roller blind, the slipclutch comprising: a clutch base, said clutch base including a shaftportion; a drive sprocket rotationally mounted on said clutch base, saiddrive sprocket engageable with a chain or cord that operate to impartrotational movement to said drive sprocket, said drive sprocketincluding a drive tube receivable about said shaft portion of saidclutch base; at least one clutch spring, said clutch spring in the formof a coil spring frictionally engaged about said shaft portion of saidclutch base and positioned between said shaft portion and said drivetube, said spring including end members that engage said drive tube suchthat rotation of said drive tube about said shaft portion is resisted bythe frictional engagement of said clutch spring about said shaftportion; and a roller tube connector secured about said drive tube suchthat said roller tube connector and said drive tube rotate togetherabout said shaft portion, said roller tube connector free from contactwith said clutch spring, rotation of said drive tube in either directioncausing said drive tube to apply a force to said clutch spring in adirection such that encourages an increase in the diameter of saidspring to thereby reduce the frictional engagement of said clutch springwith said shaft portion.
 2. The slip clutch as claimed in claim 1including two or more clutch springs.
 3. The slip clutch as claimed inclaim 1, wherein said drive tube contains one or more axial slots forreceiving said end members of said coil spring, said one or more axialslots dimensioned such that only one of said end members of said clutchspring contacts said drive tube at any one point in time.
 4. The slipclutch as claimed in claim 3, wherein said roller tube connector isreceived axially about the exterior surface of said drive tube, saiddrive tube including a second axial slot, independent from said one ormore axial slots receiving said end members of said drive spring, theinterior of said roller tube connector including a tab received withinsaid second axial slot on said drive tube thereby permitting said rollertube connector to rotate together with said drive tube about said shaftportion.
 5. The slip clutch as claimed in claim 4, wherein said tabwithin said roller tube connector is metal or has a metal covering. 6.The slip clutch as claimed in claim 4 including a bushing received aboutthe interior of said drive tube, said bushing preventing said tab ofsaid roller tube connector from contacting said clutch spring, said endmembers of said clutch spring engaging said bushing to prevent theimpingement of said end members within said drive tube.
 7. The slipclutch as claimed in claim 6, wherein said bushing is comprised of ametal.